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Closure Compiler is a JavaScript optimizing compiler. It parses your JavaScript, analyzes it, removes dead code and rewrites and minimizes what's left. It also checks syntax, variable references, and types, and warns about common JavaScript pitfalls. It is used in many of Google's JavaScript apps, including Gmail, Google Web Search, Google Maps, and Google Docs.
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/*
 * Copyright 2006 The Closure Compiler Authors.
 *
 * Licensed under the Apache License, Version 2.0 (the "License");
 * you may not use this file except in compliance with the License.
 * You may obtain a copy of the License at
 *
 *     http://www.apache.org/licenses/LICENSE-2.0
 *
 * Unless required by applicable law or agreed to in writing, software
 * distributed under the License is distributed on an "AS IS" BASIS,
 * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
 * See the License for the specific language governing permissions and
 * limitations under the License.
 */

package com.google.javascript.jscomp;

import static com.google.common.base.Preconditions.checkState;

import com.google.common.annotations.GwtIncompatible;
import com.google.common.collect.Iterables;
import java.io.IOException;
import java.io.InputStream;
import java.io.StringReader;
import java.util.HashMap;
import java.util.Map;
import javax.xml.XMLConstants;
import javax.xml.parsers.ParserConfigurationException;
import javax.xml.parsers.SAXParser;
import javax.xml.parsers.SAXParserFactory;
import org.jspecify.nullness.Nullable;
import org.xml.sax.Attributes;
import org.xml.sax.ContentHandler;
import org.xml.sax.EntityResolver;
import org.xml.sax.InputSource;
import org.xml.sax.Locator;
import org.xml.sax.SAXException;
import org.xml.sax.XMLReader;

/**
 * A MessageBundle that parses messages from an XML Translation Bundle (XTB)
 * file.
 *
 * TODO(moz): Make this GWT compatible.
 */
@GwtIncompatible("Currently not used in GWT version")
@SuppressWarnings("sunapi")
public final class XtbMessageBundle implements MessageBundle {
  private static final SecureEntityResolver NOOP_RESOLVER
      = new SecureEntityResolver();

  private final Map messages;
  private final JsMessage.IdGenerator idGenerator;

  /**
   * Creates an instance and initializes it with the messages in an XTB file.
   *
   * @param xtb  the XTB file as a byte stream
   * @param projectId  the translation console project id (i.e. name)
   */
  public XtbMessageBundle(InputStream xtb, @Nullable String projectId) {
    this.messages = new HashMap<>();
    this.idGenerator = new GoogleJsMessageIdGenerator(projectId);

    try {
      // Use a SAX parser for speed and less memory usage.
      SAXParser parser = createSAXParser();
      XMLReader reader = parser.getXMLReader();
      Handler contentHandler = new Handler();
      reader.setContentHandler(contentHandler);
      reader.parse(new InputSource(xtb));
    } catch (ParserConfigurationException | IOException | SAXException e) {
      throw new RuntimeException(e);
    }
  }

  // Inlined from guava-internal.
  private static SAXParser createSAXParser()
      throws ParserConfigurationException, SAXException {
    SAXParserFactory factory = SAXParserFactory.newInstance();
    factory.setValidating(false);
    factory.setXIncludeAware(false);
    factory.setFeature(
        "http://xml.org/sax/features/external-general-entities", false);
    factory.setFeature(
        "http://xml.org/sax/features/external-parameter-entities", false);
    factory.setFeature(
        "http://apache.org/xml/features/nonvalidating/load-external-dtd",
        false);
    factory.setFeature(XMLConstants.FEATURE_SECURE_PROCESSING, true);

    SAXParser parser = factory.newSAXParser();
    XMLReader xmlReader = parser.getXMLReader();
    xmlReader.setEntityResolver(NOOP_RESOLVER);
    return parser;
  }

  @Override
  public JsMessage getMessage(String id) {
    return messages.get(id);
  }

  @Override
  public JsMessage.IdGenerator idGenerator() {
    return idGenerator;
  }

  @Override
  public Iterable getAllMessages() {
    return Iterables.unmodifiableIterable(messages.values());
  }

  /**
   * A {@link ContentHandler} that creates a {@link JsMessage} for each message
   * parsed from an XML Translation Bundle (XTB) file.
   */
  private class Handler implements ContentHandler {
    private static final String BUNDLE_ELEM_NAME = "translationbundle";
    private static final String LANG_ATT_NAME = "lang";

    private static final String TRANSLATION_ELEM_NAME = "translation";
    private static final String MESSAGE_ID_ATT_NAME = "id";

    private static final String PLACEHOLDER_ELEM_NAME = "ph";
    private static final String PLACEHOLDER_NAME_ATT_NAME = "name";

    String lang;
    JsMessage.@Nullable Builder msgBuilder;

    @Override
    public void setDocumentLocator(Locator locator) {}

    @Override
    public void startDocument() {}

    @Override
    public void endDocument() {}

    @Override
    public void startPrefixMapping(String prefix, String uri) {}

    @Override
    public void endPrefixMapping(String prefix) {}

    @Override
    public void startElement(String uri, String localName, String qName,
                             Attributes atts) {
      switch (qName) {
        case BUNDLE_ELEM_NAME:
          checkState(lang == null);
          lang = atts.getValue(LANG_ATT_NAME);
          checkState(lang != null && !lang.isEmpty());
          break;
        case TRANSLATION_ELEM_NAME:
          checkState(msgBuilder == null);
          String id = atts.getValue(MESSAGE_ID_ATT_NAME);
          checkState(id != null && !id.isEmpty());
          msgBuilder = new JsMessage.Builder().setKey(id).setId(id);
          break;
        case PLACEHOLDER_ELEM_NAME:
          checkState(msgBuilder != null);
          String phRef = atts.getValue(PLACEHOLDER_NAME_ATT_NAME);
          msgBuilder.appendCanonicalPlaceholderReference(phRef);
          break;
        default: // fall out
      }
    }

    @Override
    public void endElement(String uri, String localName, String qName) {
      if (TRANSLATION_ELEM_NAME.equals(qName)) {
        checkState(msgBuilder != null);
        if (!msgBuilder.hasParts()) {
          msgBuilder.appendStringPart("");
        }
        String key = msgBuilder.getKey();
        messages.put(key, msgBuilder.build());
        msgBuilder = null;
      }
    }

    @Override
    public void characters(char[] ch, int start, int length) {
      if (msgBuilder != null) {
        String part = String.valueOf(ch, start, length);
        // Append a string literal to the message.
        msgBuilder.appendStringPart(part);
      }
    }

    @Override
    public void ignorableWhitespace(char[] ch, int start, int length) {
      if (msgBuilder != null) {
        // Preserve whitespace in messages.
        msgBuilder.appendStringPart(String.valueOf(ch, start, length));
      }
    }

    @Override
    public void processingInstruction(String target, String data) {}

    @Override
    public void skippedEntity(String name) {}
  }

  /**
   * A secure EntityResolver that returns an empty string in response to
   * any attempt to resolve an external entity. The class is used by our
   * secure version of the internal saxon SAX parser.
   */
  private static final class SecureEntityResolver implements EntityResolver {

    @Override
    public InputSource resolveEntity(String publicId, String systemId) {
      return new InputSource(new StringReader(""));
    }
  }
}